555 TIMER IS AN IC(INTEGRATED CIRCUIT) USED AS A TIMER ,PULSE GENERATOR AND OSCILLATOR.
TYPES:
1-MONOSTABLE
2-BISTABLE ASTABLE
3-ASTABLE
555 TIMER IC HAS 8 PIN IN NE555 AND 14 PINS IN 556 ETC
MONOSTABLE:HAVING ONE STABLE STATE
ASTABLE:HAVING NOSTABLE STATE.
BISTABLE:HAVING TWO STABLE STATES
BISTABLE CAN BE USED AS A FLIP FLOP.